f address euguen's nit from #986 (comment)

Author: TheBlueMatt

02-peer-protocol.md

@@ -510,7 +510,8 @@ The sender:
       - SHOULD initially set `alias` to value not related to the real `short_channel_id`.
     - otherwise:
       - MUST set `alias` to a value not related to the real `short_channel_id`.
-    - MUST NOT send the same `alias` for multiple peers.
+    - MUST NOT send the same `alias` for multiple peers or use an alias which
+      collides with a `short_channel_id`  of a channel on the same node.
     - MUST always recognize the `alias` as a `short_channel_id` for incoming HTLCs to this channel.
     - if `channel_type` has `option_scid_alias` set:
       - MUST NOT allow incoming HTLCs to this channel using the real `short_channel_id`